Habitat

Agile opossums are an arboreal species that have been found in both wet and dry forests; however, they are more common in dry and seasonally dry forests south of the Amazon in Brazil, Paraguay, Bolivia and Argentina. Their habitats include humid and evergreen forests in the lowland understory, at elevations up to 1,800 meters. Agile opossums have also been found in both caatinga and cerrado biomes, which are characterized by thorny bushes and gallery forests, respectively. In addition, this species is also tolerant of habitat degradation caused by humans. These animals are often found on vines and tree branches, 1.5 to 2 meters off the ground. (Carmignotto, et al., 2011; Creighton and Gardner, 2008; Geise and Astua, 2009; Voss, et al., 2009)

Physical Description

Agile opossums are small, pouchless marsupials with reddish brown to dusky gray dorsal pelage and white to gray ventral pelage. They have a thin, dark ring around their eyes, which does not extend to their nose. These animals are adapted for an arboreal lifestyle, as evidenced by the elongated digits on their feet. Likewise, they have a long, hairy, grizzled-brown prehensile tail, which is about 123 mm long, with a tail-to-body ratio of about 1.4. Their approximate total body length is 212 mm and their large hind feet are approximately 15 mm long. This species is small and sexually dimorphic, where males are larger than females. Agile opossums weigh between 13 to 21 grams. Members of the genus Gracilinanus may grow lifelong, these species are short-lived; however, the rare individuals that survive multiple years tend to be noticeably larger. In general, the temperature and metabolic rate of didelphids tends to be lower than similarly sized placental mammals. Agile opossums tend to have a body temperature of approximately 33 °C, with a basal metabolic rate similar to other marsupials. Due largely to their range overlap, agile opossums are often mistaken for their relative, Brazilian gracile opossums. In addition to their thinner ocular ring, agile opossums can be distinguished by their smaller ears and tails. (Carmignotto, et al., 2011; Cooper, et al., 2009; Creighton and Gardner, 2008; Diaz, et al., 2002; Geise and Astua, 2009; Pires, et al., 2010; Voss, et al., 2009)

Reproduction

Agile opossums engage in a polygynous mating system, similar to other didelphids. The extreme competition among males for breeding females causes a massive amount of stress for this species. As a result, agile opossums are considered partially semelparous because many of the males die shortly after breeding. This trend is considered only partial because a few males do survive to a second or even third breeding season. (Cooper, et al., 2009; Fernandes, et al., 2010; Martins, et al., 2006a)

There is very little information specifically regarding the reproductive behavior of agile opossums; however, research has shown that a female may have up to 12 young with her at a time. Much more research has been conducted on their close relative, Brazilian gracile opossums. It is not known whether these species share all reproductive traits, however, given that they share a similar range and both are solitary, nocturnal and arboreal, it is not unlikely that these species share reproductive traits as well. Brazilian gracile opossums begin mating when they are about 1 year old. This species reproduces seasonally; females are receptive during the end of the cool dry season, from August to September. Several pregnant and lactating females have been captured in September to December. Brazilian gracile opossums' strategy of synchronous estrous means that their young are born in October to December, during the first half of the warm wet season when insect prey are most populous. This likely optimizes the female’s ability to capture food while caring for young. Weaning begins at about 2 to 3 months of age when the young weigh about 8 to 10 grams. (Carmignotto, et al., 2011; Martins, et al., 2006a; Martins, et al., 2006b; Pires, et al., 2010)

Lifespan/Longevity

This species has a short lifespan; in general, their life expectancy is about 1 to 1.5 years. Agile opossums are considered partially semelparous; most males do not survive to a second breeding season. Among Brazilian gracile opossums, a close relative of agile opossums, males invest so much in competing for mates that they often show fur loss, poor body condition and are more likely to become infested with parasites after the beginning of the breeding season. Although females also have a short lifespan, they survive to a second year more frequently than males. In general, offspring from the preceding season replace the adults each year. (Cooper, et al., 2009; Martins, et al., 2006a; Martins, et al., 2006b; Pires, et al., 2010)

Behavior

Agile opossums are solitary and nocturnal; they typically only come together for breeding, these animals may forage in a similar location, but do not interact. This species enters torpor when the ambient temperature is colder than 20°C. Agile opossums are arboreal and have been trapped on tree branches and vines 1.5 to 2 meters above ground, but also forage on the ground. (Carmignotto, et al., 2011; Cooper, et al., 2009; Hershkovitz, 1992)

Communication and Perception

There is very little information regarding the communication or perception of genus Gracilinanus. Members of this genus may produce a variety of sounds defensively or when they are startled, these sounds include hissing, growling and screeching. It has been suggested that arboreal marsupials are more vocal and have more adept vision than their non-arboreal counterparts; however, no conclusive studies have been conducted. (Bradshaw, et al., 1998; Delciellos and Vieira, 2009; Hershkovitz, 1992)

Ecosystem Roles

Agile opossums are insectivores and important seed dispersers. Likewise, they are parasitized by a variety of nematodes including Pterygodermatites jagerskioldi, Spirura guianensis, Physaloptera herthameyerae and members of genus Gracilioxyuris. These parasites were recovered from the esophagus, stomach and intestines of agile opossums. It is hypothesized that this species is particularly vulnerable to parasitism due to their diet. (Feijo, et al., 2008; Torres, et al., 2007; Torres, et al., 2009)

Ecosystem Impact

disperses seeds

Commensal/Parasitic Species

nematodes (Pterygodermatites jagerskioldi)

nematodes (Spirura guianensis)

nematodes (Physaloptera herthameyerae)

nematodes (Gracilioxyuris)

Economic Importance for Humans: Positive

Although they are important seed dispersers within their habitat, agile opossums have no known positive impacts on human populations.

Economic Importance for Humans: Negative

There are no known negative impacts of agile opossums on human populations.

Conservation Status

Agile opossums are currently listed as a species of least concern according to the IUCN Red List of Threatened Species. Their large range, population size and their ability to live in human-altered habitats makes the outlook for this species positive and stable. (Carmignotto, et al., 2011)

Contributors

Glossary

living in the southern part of the New World. In other words, Central and South America.

acoustic

uses sound to communicate

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

polygynous

having more than one female as a mate at one time

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

semelparous

offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

Hershkovitz, P. 1992. The South American gracile mouse opossums, genus Gracilinanus Gardner and Creighton, 1989 (Marmosidae, Marsupialia) a taxonomic review with notes on general morphology and relationships. Field Zoology, 70:1: 1-56.

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This material is based upon work supported by the
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Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.